Intermediate frequency transformer



Dec. 5, 1944.` R. L HARVEY INTERMEDIATE FREQUENCY TRANSFORMER Filed Oct. 50, 1940 Patented Dec. 5, 1944 INTERMEDIATE FREQUENCY TRANSFORMEB Robert L. Harvey, Collingswood, N;

Radio Corporation of Delaware J., assignor to of America, a corporation Application October 30, 1940, Serial No. 363,538

Claims.

This invention relates to intermediate frequency transformers and has for its primary object to provide such a transformer which is (1) variably tunable by means of movable magnetic core elements without appreciably changing the coupling relation between the transformer windings, and (2) provided with means for adjusting or determining the coupling relation between said windings without appreciably varying the tuning of said windings.

It is a further object of the present invention to provide an improved 'coupling transformer for intermediate frequency 'signal circuits and the like, which provides the adjustment features above referred to with a high degree of stability and which is at the same time compact and readily manufactured at low cost.

The invention will, however, be further understood from the following description when con'- sidered in connection with the accompanying drawing and its scope is pointed out inthe appended claims. I y Inthe drawing.'

Figure l is a View partly in cross-section of a transformer embodying the invention and con nected` in circuit pling device, and

Figure ,2 is a similarcross-sectional view of a transformer also embodying the invention, as a modification of the device shown in Fig. l.

Referring to Flg. 1, the transformer 5 may be considered as an* lnterstage coupling transformer for an intermediate frequency amplifier connect ed between a first stage 1 and a second stage 8. 'I'he output circuit 9 of the first' stage 1 includes a multilayer solenoid coupling winding or primary I0 while the input cr grid circuit II of the stage 8 includes a second multilayer solenoid coupling winding or secondary I 2.

The primary I0 is connected to input terminals I3 and I4 as indicated, across which there may be connected a' suitable fixed tuning capacitor I5 for resonating the winding Ill as a tunableinductanceV within a 'predetermined frequencyrange within which it is accuratelyI tuned by an axially movable magnetic coremember I6. Th core I 6 is movable into means such-as a threaded rodor adjustment as an interstage amplifier couscrew I1 carried by ,a supporting end'member I8l atone end of the transformer. 'I'he winding I0 isf supported by an insulatingtubularcoil" form I9 maintained centrally of the transformerl in suitable recesses at one end :in the member I v8' as indicated at 2li andin corresponding recesses 2I in a similar supporting end-member onthe'opposite end of the coil asxindicated at 22;`l

The members I8 and 22'are supported in spaced relation to each otherby a metallic casing 23 forming an outer electrostatic shield for the winding and this, in turn, is slidably mounted in a andvout ofthe winding by suitab I the other.

tubular bracket 24 provided with mounting means 25 by which it may be attached to any suitable supporting means.

The secondary I2 is similarly mounted in a slidable unit comprising a similar metallic outer casing 21 having spacing and supporting end members 28 and 29 for the insulating coil form 30 extending between them. Output terminals SI and 32 for the secondary are provided in the end member 28 and said terminals are connected to a suitable tuning capacitor 33 also effective to tune the secondary Within the operating frequency range of the circuits with which the transformer is used. The final tuning is accomplished as in the case of the primary, by means of a movable magnetic core member 34 having an adjusting screw 35 supported by the end member 28.

The coupling windings I0 and I2 are provided with radially outer core members 36 and 31 of magnetic material whichare preferably annular members .fixed in relation to the windings but relatively adjustable axially one with respect to The outer cores are insulated from the outer casings 23 and 21 by layers of insulating material 38`and 39 forming a lining for the casings 33 and 21 and from the inner cores I3 and 34 by the coll forms I9 and 30.

It will be noted that the outer core members 33 and 31, the coils I 0 and I2 and thelnner cores I6 and 34 are all arranged in coaxial relation to each other and that said coils and inner core elements are more widely spaced from each other inan axial direction than the outer core members 36 and 31; that is, the latter members are more closely spaced than the windings I0 and I2 or the tuning cores I6 and 34. elements, the tuning cores By so arranging said I6 and 34 may be moved to tune the windings effectively without appreciably changing the coupling between the windings as determined by the relative positions or spacing `of the outer core elements 36 and 31.

In order to adjust 'this relation to providea predetermined or optimum coupling between the primarywand secondary windings lof' the trans-v former unit, the primary unit 23 and the secondary unit 21 are relatively movable in the supporting bracket 24 and when adjusted for proper coupling may be secured in position, one relative to the other, by means of solder-or other securing meansv as indicated at 40 to lock the outer casings 23 and' 21 tothe bracket or sleeve 24.

In operation, Ithe outer core members 31 are more Aclosely spaced,l onefwith respect to the othenatl al1 timesf-thanthe inner cores' I 4 and -34 ffor'determining the coupling between the windings,` `whereby theinner cores may be adjusted substantially without Jchanging the coupling relation established by adjustment of the outer cores.

Referring now to Fig. 2, a modification of the 36 and Y construction shown in Fig. 1 comprising the transformer coils or windings 50 and 5I are each provided with inner movable tuning cores, as indicated at 52 and 53, and annular outer cores, as shown at 54 and 55. The latter are constructed substantially to surround a major portion oi.' the winding and to form a closure for the adjacent ends of the windings as indicated at II and 51. The spacing between the cores 54 and 55 is determined by the thickness of an insulating disc 58 located between the two winding units. This is made in production to provide a desired coupling between the windings 50 and Il. Thus, in the present embodiment, the outer cores are depended upon for determining and providing the coupling between the two windings and are therefore more closely spaced than either the windings or the inner movable tuning cores.

In the present example, the outer cores, as well as the inner cores, are insulated from an outer shield container or casing il by cylindrical insulating sleeves l and 6I between which the terminal conductors 83 and 64 are secured. The movable cores are supported on threaded adjustment screws 65 mounted in insulating and supporting members 86 at each end of the transformer. This may be of any suitable insulating material.

The cores 52 and 53 are preferably of molded iron powder with a suitable binder while the outer cores 54 and 55 preferably contain a larger percentage of insulating binder.

It will be noted that all of the core elements are insulated, one from the other, thereby cutting down conductive current paths through the core structure and to reduce capacity eiects or stray capacity in shunt with the windings. As in the preceding embodiment, the coil forms 61 for the primary and secondary are of suitable insulating material.

The tuning capacitors for the windings are provided by including the conductive end members 'Il and 1| of the terminals 63 and il between the supporting member 86 and an insulating end plate 13 with a washer 1l of dielectric material between them. A similar capacitor arrangement is provided at l at the opposite end of the transformer for tuning the winding 5i, the terminals of which are at right angles to those shown in the drawing, and hence do not appear. However, as the details of construction do not concern the present invention, further description is not believed to be necessary.

I claim as my invention:

1. A coupling transformer for high frequency circuits, comprising a pair of coaxial spaced solenoid windings, an. inner axially movable tuning core of magnetic material for each of said windings, means providing radially outer coaxial cores of magnetic material for said windings, at least f -a portion of each of said outer cores providing appreciable magnetic leakage for coupling to the other of said outer cores, and said outer cores being relatively axially adjustable and being more cloly spaced at all times, one withrrespect to the other, than the inner tuning cores and windings for determining the degree of coupling between said windings and said windings being more closely spaced than said inner cores.

2. A coupling transformer for tuned high frelquency circuits comprising a pair of Vtunable inductance windings in coaxial spaced relation to each other, an inner axially movable tuning core of magnetic material for each of said windings.

means providing a radially outer core surroundllo ing each of said windings in axially spaced relation to each other, at least a portion of'each oi!- said outer cores providing appreciable magnetic leakage for coupling to the other of said' outer cores, and said outer cores being relatively axially adjustable and being more closely spaced at all times than the inner tuning cores and said windings for determining the degree of. coupling between said windings and said windings being more closely spaced than said inner cores, a metallic shield casing surrounding said windings and cores, and means for insulating said cores and casing one from another.

3. A transformer for coupling tuned high frequency circuits which comprises a pair of coupling windings in coaxial spaced relation to eachv other, means providing an inner movable tuning core of magnetic material for each of said windings, means providing outer core members of magnetic material surrounding each of said windings in axially spaced relation to each other, at least a portion of each of said outer cores providing appreciable magnetic leakage for coupling to the other of said outer cores, and said outer core members being relatively axially adjustable and being more closely spaced at all times than the inner tuning cores, for determining the degree of coupling between said windings, and said windings being more closely spaced than said inner cores and said inner tuning cores being thereby adjustable substantially without changing the coupling relation between said windings as determined by adjustment of the outer core means.

4. A coupling transformer for high frequency circuits comprising a pair o! coupling windings mounted in coaxial spaced relation to each other, means providing inner coaxial adjustable cores of magnetic material for each of said windings, an outer annular core of magnetic material surrounding each of said windings, at least a portion of each of said outer cores providing appreciable magnetic leakage for coupling to the other means providing. inner movable coaxial cores of magnetic material for each of said windings, an outer annular core ot magnetic material surrounding each of said windings at least adjacent ends of said outer coresl being closed, and at least said closed core portions providing appreciable magnetic leakage for coupling to the other oil-said closed core portions, means for axially spacing said closed ends of said outer cores to determine the degree of coupling between said windings, and said windings being more closely spaced than said inner cores and said inner cores and windings being at all times more widely spaced than said outer cores, whereby the tuning of said windings by. adjustm/ent of said inner cores may be effected substantially without changing the coupling relation between said windings as established by adjustment of the outer cores.

ROBERT L. HARVEY. 

